3,4-methylenedioxymethamphetamine (MDMA or "ecstasy") use has soared in the past few years despite increasing scientific evidence of adverse consequences. MDMA is perceived as safe by many users despite media reports of deaths and serious medical complications. The mechanism(s) underlying the reported consequences of MDMA use (e.g. hyperthermia, disrupted sleep, mood and anxiety problems) are not known. The goal of the proposed studies is to define both the acute and chronic consequences of MDMA use in humans. Controlled laboratory administration of MDMA (2 mg/kg) will be used to assess the acute effects of MDMA on physiological (thermoregulation, metabolism, and sleep), psychological (mood, anxiety), and cognitive parameters. For an evaluation of chronic effects of MDMA use on mood and anxiety symptoms and cognitive measures, a longitudinal study will be conducted. Specific Aim 1 is to determine the effect of MDMA (compared to placebo) on thermoregulation and metabolism under different ambient temperatures (18 and 30 deg C) or under different activity levels (bed rest and moderate exercise [40 percent max V02] for 60 minutes at 23 deg C). Specific Aim 2 is to directly measure the effect of MDMA (compared to placebo, d-amphetamine, or partial sleep deprivation) on sleep time and architecture, cognitive function, mood, subsequent day mood, sleepiness, and cognitive function. Specific Aim 3 is to longitudinally measure cognitive function and psychopathology in novice (1-5 exposures) MDMA users over a two-year period, following an extensive baseline evaluation. The long-term goal of these studies is to provide reliable information about the extent and basis for MDMA-related acute and long-term adverse health consequences. This information will be applied to develop and test strategies to block the effects or at least minimize consequences.